Clinically Anaesthetic Hazards & Scavenging Flashcards
Anaesthetic breathing systems are used for what purpose?
- to deliver oxygen &/or anesthetic agent and remove CO2
- to prevent rebreathing of CO2
What are the three ways of classifying breathing systems?
- with or without soda lime
- Mapleson classification
- Open, closed, semi-open/semi-closed
Soda lime systems are NOT
passive scavenging
What is the purpose of soda lime?
to absorb CO2 and allowing exhaled air to be re-utilised
soda lime produces
heat & water
soda lime should contain
an indicator to show when exhausted
What are some disadvantages of soda lime?
- dehydrated when mixed w/ halogenated compounds and can produce carbon monoxide
- compound A can be produced which is a nephrotoxic agent when using sevoflurane
- color change is only temporary and can revert (must be read when still warm)
What breathing systems use soda lime?
- circle
- & technically to-and-fro (not used anymore)
What is the main feature of circle breathing systems?
- unidirectional valves & soda lime canister so everything flows in 1 direction
if valve get sticky and doesn’t close properly in a circle system, what is the main consequence?
the patient will exhale CO2 to both sides and thus on the next inspiration will inhale CO2 from the inspiratory limb leading to massive CO2 inhalation very suddenly…
When the soda lime is exhausted, what does it do to CO2 and how does it affect vitals?
- slow rebreathing of CO2 occurring
- numbers change slowly
inhaled gas in a circle system consists of…
a mix of previously exhaled gas from which CO2 has been removed & variable fresh gas flow from a common gas outlet that includes oxygen and an anesthetic agent
In circle systems, FGF should be at what level when first establishing anesthetic depth?
- it should be high to establish sufficient anesthetic concentrations in the system and anesthetic depth
if maintenance FGF is started at during anaesthesia, it is…
only enough to maintain sufficient oxygenation of P where the majority of air inhaled is exhaled air w/ no anesthetic agent and is only getting a tiny fraction of inhaled anesthetic agent
maintenance FGF must be adequate to replace
oxygen required for cellular metabolism, but only enough needed to maintain that lost per breath
What is the recommended initial FGF that should be used in a circle system?
100 ml/kg/min
When anesthetic depth is increased, what is the recommended FGF that should be used in a circle system?
100 ml/kg/min
How long should an animal on a circle system be given the recommended initial dose of FGF?
first 10-15 minutes of anaesthesia with the pop-off valve completely open and exhaled air completely leaves system
What is the recommended FGF in a circle system?
10-20 ml/kg/min
(however, most vaporizers req a minimum FGF of 500 ml/min for accuracy)
What 2 things in a circle system increase the system’s resistance?
unidirectional valves and soda lime
What size animal can be used on a circle system?
> 8-10 kg
When a circle system is used, how is the patient’s body temperature impacted?
the inspired gas is warmed and moistened so the patient is less hypothermic, but could lead to hyperthermia
can help keep P warm during maintenance phase
In a circle system, the concentration of inspired gas is NOT the same as
the vaporiser b/c there is a discrepancy between the vaporizer and the patient concentration thus it is lower in the patient than the vaporizer unless it is a really long procedure
concentration of inspired gas in a circle system CANNOT be
altered rapidly unless you increase FGF
What occurs in a circle system when the patient is breathing against increased resistance for long periods?
weak respiratory muscles so efficiency of ventilation decreases
When can a patient <8 kg receive a circle system?
If they need positive pressure ventilation
What are causes for rebreathing of CO2 in a circle system?
Exhausted soda lime
leaky unidirectional valves
What are the 3 types on non-rebreathing systems?
Ayre’s T-piece (& mods)
Bain (co-axial or parallel)
Lack (mini-lack)
What 2 pieces are missing from a non-rebreathing system that are present in a circle system?
No soda lime
No unidirectional valves
How do you rid a non-rebreathing system of CO2?
through high FGF
During the expiratory phase of a non-rebreathing system, the high FGF must…
push all exhaled gases out of the system prior to the next inhalation
What are the advantages of a non-rebreathing system in comparison with a circle system?
- Concentration of inspired gas is the same as the vaporizer
- concentration of inspired gas may be altered rapidly (w/I 1-2 breaths)
What are the disadvantages of a non-rebreathing system in comparison with a circle system?
- more costly to run (uses more O2 & vapor)
- causes more atmospheric pollution
- high gas flow contributes to P hypothermia
What are the 4 main pieces of a Ayre’s T-piece?
- fresh gas limb
- reservoir limb
- APL valve
- reservoir bag
How do you calculate the FGF for an Ayre’s T-piece?
2.5-3 x minute volume of the P (about 200 ml) = 500-600 ml/kg/min
What patient size is recommended to use the Ayre’s T-piece?
P size <10 kg, with no lower weight limit
Can you use IPPV w/ an Ayre’s T-piece?
Yes, highly recommended b/c more efficient and preserves FGF
What are some causes for rebreathing of CO2 in an Ayre’s T-piece?
- Insufficient FGF, not enough time to flush CO2 out properly
- shortened expiratory phase (tachypnoeic)
- excessive equipment dead space
What are the three main pieces of a Bain non-rebreathing system?
- fresh gas limb inside the reservoir limb
- APL valve
- Reservoir bag
What should the FGF be for a Bain non-rebreathing system?
1.2-3 x Minute vol of P = 300-400 ml/kg/min
A bain non-rebreathing system can be used in what size of patient?
> 10kg, up to 25 kg
Can IPPV be used in Bain system?
Yes, recommended to decrease FGF
What are causes of rebreathing of CO2 in the Bain system?
- insufficient FGF
- shortened expiratory pause
- leak in the inner FGF limb–> enormous dead space causing rein halation of CO2
What patient size can be used in a mini-lack system
3-10 kg
Which non-rebreathing system is the most efficient?
Mini-lack
What is the FGF recommended for use in mini-lack system?
0.8-1 x minute volume of p = 160-200 ml/kg/min
Can IPPV be used with a mini-lack non-rebreathing system?
No!
When does gas flow need to be altered when using systems w/o soda lime?
- if the minute volume increases
- if capnography is used
- if IPPV is used
When using a non-rebreathing system, do you need to alter FGF when you increase the depth of anaesthesia?
NO!
The efficiency of breathing system is demonstrated by…
the rebreathing of CO2
What is the equation for the minute volume of a patient?
RR x TV = MV
if you are not using a capnograph, you should always use
a high level of FGF
A scavenging system must be able to…
collect waste gases from the exhaust port of the anesthetic circuit & dispose of them outside the working environment
What does the scavenging valve also known as?
pressure-relief valve
pop-off valve
spill valve
exhaust valve
What is an adjustable pressure limiting valve?
- special type of scavenging valve which prevents build-up of extremely high pressures
- aka more sophisticated pop-off valve
What is active scavenging?
- exhaled gas is actively extracted from breathing system & expelled to the atmosphere
- creates a vacuum & sucks out anesthetic & dumps outside
What are the 3 components required in active scavenging?
- scavenging valve of breathing system
- connected to 22 mm tubing (in Europe)
- attached to air-break/receiver which is connected to extractor fan (vacuum), through which the gas is vented to the atmosphere outside
What is the main interface between the breathing system and the active disposal system that must protect the lung’s from excessive negative pressures in an active scavenging system?
Air brake
What is passive scavenging?
No extractor is used to remove exhaled gas; driven solely but eh patient’s respiratory efforts
in a passive scavenging system, it is important that there is
no massive resistance in the tubing
When putting tubing out a window in a passive scavenging system, what is important to remember?
- end of tubing must be at the same level as the scavenging valve or lower because anesthetic gases are heavier than air & will sink & not get out of the tubing
When putting tubing out a window in a passive scavenging system, what is an important caution?
- the tubes can get blocked
- complete block = exhalation impossible
- partial block = inhalation/exhalation difficult
Aside from a tube out the window, what is another form of passive scavenging?
Activated charcoal
How does activated charcoal passive scavenging work?
Exhaled air goes through scavenging (activated charcoal), and the halogenated gases (anesthetic) is absorbed into the charcoal and CO2 & O2 are exhaled into the room
What is important to remember about activated charcoal?
- absorbs halogenated gases, but does not render them inert & heating of the canister will release them
- does NOT absorb N2O
How do you know activated charcoal is exhausted?
It’s weight reaches the max weight on the canister which is heavier than it was when it was fresh
How can you minimize workplace pollution w/ anesthetic agents?
- check scavenging system
- intubate P’s w/ cuffed ETT & inflate cuff
- avoid face mask & induction chamber inductions
- connect breathing system before turning on anesthetic vapors & turn gases off for any disconnections (Even short-term) & cap off to prevent gases escaping into the room
- clear breathing system from anesthetic vapors w/ high O2 flow before disconnection (5 min)
- fill vaporizers at end of day to minimize exposure
- ventilate induction, operating, recovery areas
- service equipment regularly
- monitor theatre pollution at least q 2 yrs
- leak test breathing system to prevent gases into room
What are some short-term signs of exposure to high concentration of volatile agents?
- headache
- irritability
- fatigue
- nausea
- drowsiness
- difficulties w/ judgement & coordination
- liver & kidney dz
What are occupational exposure standards in IE?
Halothane: 10 ppm
Isoflurane: 50 ppm
N2O: 100 ppm
Sevoflurane: 60 ppm
What are the hazards of ketamine injection?
hallucinations, convulsions, paralysis
long-term abuse –> brain atrophy/degeneration of white matter, decreased sociability, attention deficit, impaired memory recall/flashbacks; psychosis/ schizophrenia if predisposed
what are the hazards of opioids?
abuse & addiction
resp depression
What are the hazards of alpha-2 agonists?
CV alterations, resp depression
What are hazards of Etrophine/ Immobilon?
severe resp depression, coma, death
